If R, C and L are fundamental quantities in a circuit like resistance, capacitance and inductance in W, then find dimensional formula for resistance and capacitance.

Dimensional analysis can be defined as the practice of studying relations between physical quantities by recognising the dimensions of them. These dimensions are independent of numerical multiples and similar constants. The quantities present in the world can be described as a function of the fundamental dimensions.

Dimensional Formula

Dimensional formula of a quantity is the expression indicating the powers wherein the fundamental units are to be increased to obtain one unit of a derived quantity. For instance, if Q is an unit of a derived quantity which is defined by Q = MaLbTc, then MaLbTc is known as the dimensional formula with exponents a, b and, c that are called the dimensions.

Dimensional Formula for Resistance

The dimensional formula of resistance can be expressed as:

M1 L2 T-3 I-2

Here,

  • M = Mass
  • I = Current
  • L = Length
  • T = Time

Resistance (R) = Voltage × Current-1 … [1]

Now, because, Voltage (V) = Electric Field × Distance = [Force × Charge-1] × Distance

Accordingly, dimensional formula of charge = current × time = I1 T1

Dimensional formula of voltage = [Force × Charge-1] × Distance

= [M1 L1 T-2] × [I1 T1]-1 × [L1]

= [M1 L2 T-3 I-1] … [2]

On replacing equation (ii) in equation (i) we get,

Resistance (R) = Voltage × Current-1

R = [M1 L2 T-3 I-1] × [I]-1 = [M1 L2 T-3 I-2]

Hence, resistance is dimensionally depicted as M L2 T-3 I-2.

Dimensional Formula of Capacitance

The dimensional formula of Capacitance is expressed by:

M-1 L-2 T4 I2

Here,

  • M = Mass
  • I = Current
  • L = Length
  • T = Time

Derivation of Capacitance

Capacitance (C) = Charge × Voltage-1 . . . [1]

Since, Charge = Current × Time

∴ Therefore, the dimensional formula of charge can be give as = [I1 T1] . . . . [2]

And, Voltage = Electric Field × Distance . . [3]

Now, as per Electric Field,

Electric Field = [Force × Charge-1]

Hence, dimensional formula of force and charge equals [M1 L1 T-2] and [I1 T1] respectively.

∴ The dimensional formula of Electric Field = [M1 L1 T-2] × [I1 T1]-1

= [M1 L1 T-3 I-1] . . . [4]

On replacing equation [4] in equation [3] we can obtain,

The dimensional formula of Voltage = [M1 L1 T-3 I-1] × [L1]

= [M1 L2 T-3 I-1] . . . [5]

On replacing equations [5] and [2] in equation [1] we can obtain,

Hence, Capacitance = Charge × Voltage-1

Or, as can be expressed, C = [I1 T1] × [M1 L2 T-3 I-1]-1 = [M-1 L-2 T4 I2]

Thus, the Capacitance can be dimensionally expressed as [M-1 L-2 T4 I2].


Related Questions

  1. In An Arrangement Of Resistances, Find Effective Resistance Between Points A and B.
  2. What Is Effective Resistance?
  3. X and Y, which are two resistors, with resistances of 2 Ω and 3 Ω respectively are first connected in parallel and then in series. In both cases, the voltage that is supplied is 5 V. (i) Illustrate a circuit diagram to show the combination of resistors. (ii) Calculate the amount of voltage across 3 Ω resistor in the series combination of resistors.
  4. Find The Highest And Lowest Total Resistance Of A Combination Of Four Coils With Resistances 4 Ohms, 8 Ohms, 12 Ohms, 24 Ohms.
  5. What is Null Voltage?
  6. Draw An Electric Circuit With A Cell, Key, Ammeter, A Resistor (Series) Of 2 Ohm With a Combination Of Two Resistors (4 Ohm Each) In Parallel And A Voltmeter Across Parallel Combination.

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CBSE CLASS XII Related Questions

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                      CBSE CLASS XII Previous Year Papers

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